Fuel cells electrochemically convert fuels and oxidants to electricity and heat and can be categorized according to the type of electrolyte (e.g., solid oxide, molten carbonate, alkaline, phosphoric acid or solid polymer) used to accommodate ion transfer during operation. Moreover, fuel cell assemblies can be employed in many (e.g., automotive, aerospace, industrial, residential) environments for multiple applications.
A Proton Exchange Membrane (hereinafter “PEM”) fuel cell converts the chemical energy of fuels such as hydrogen and oxidants, such as air, directly into electrical energy. The PEM is a solid polymer electrolyte that permits the passage of protons (i.e., H+ ions) from the “anode” side of the fuel cell to the “cathode” side of the fuel cell while preventing passage therethrough of reactant fluids (e.g., hydrogen and air gases). The membrane electrode assembly is placed between two electrically conductive plates, each of which has a flow passage to direct the fuel to the anode side and oxidant to the cathode side of the PEM.
Two or more fuel cells can be connected together to increase the overall power output of the assembly. Generally, the cells are connected in series, wherein one side of a plate serves as an anode plate for one cell and the other side of the plate is the cathode plate for the adjacent cell. Such a series of connected multiple fuel cells is referred to as a fuel cell stack. The stack typically includes means for directing the fuel and the oxidant to the anode and cathode flow field channels, respectively. The stack also usually includes a means for directing a coolant fluid to interior channels within the stack to absorb heat generated by the exothermic reaction of hydrogen and oxygen within the fuel cells. The stack also generally includes means for exhausting the excess fuel and oxidant gases, as well as product water.
Many fuel cell systems include a balance of plant that supplies the necessary reactant and cooling fluids for a fuel cell or fuel cell stack. The balance of plant may include devices such as pumps, air compressors, blowers, fans, valves, and sensors. These devices function cohesively to provide power to a load, such as a stationary device or an industrial electric vehicle. In order for the fuel cell stack to achieve optimal efficiency and longevity, the reactants must be properly humidified. Compressing a fluid such as air will increase the temperature of the fluid as well as the pressure due to the isentropic and mechanical inefficiencies associated with the component. Depending on the design of the compressor and the compression ratio, this resultant temperature may be too high for downstream components, such as a humidifier.
Many fuel cell systems store fuel on board at or near room temperature. Humidification of the fuel may be accomplished by recycling saturated exhaust fuel and blending it with fuel from the fuel supply. If a warm saturated fuel were to be combined with a cool, dry fuel liquid water may be formed.
Thus, there is a need to properly condition the temperature of the reactants before they are directed to the fuel cell or fuel cell stack in order to optimize the operation of the fuel cell system.